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Melting Antarctic icebergs fight back against global warming

Iron in the meltwater from Antarctic icebergs is spurring the growth of algae that suck up carbon dioxide from the atmosphere, according to new research.

Icebergs in the Antarctic Ocean are shrinking due to global warming. New research has found that melting icebergs are depositing iron into the sea water, spurring the growth of plankton that take carbon dioxide out of the atmosphere. (Kyodo / Courtesy of the U.S. administration)

By Kenyon WallaceToronto Star

Fri., May 20, 2011

As the earth slowly loses its polar ice caps, the very ice that is melting away is putting up its own fight against global warming, surprising new research has found.

Iron in the meltwater from Antarctic icebergs is spurring the growth of algae that suck up carbon dioxide from the atmosphere and eventually deposit organic carbon on the bottom of the sea floor, according to the first comprehensive study of the phenomenon.

The five-year study, which will appear next month in a special issue of the journal Deep Sea Research Part II: Topical Studies in Oceanography, found that as the meltwater mixes with sea water, the iron fertilizes the growth of phytoplankton and algae, converting the once mineral-starved water into biological communities abundant with life.

“The nutrients contained in the meltwater come out and enhance the growth of micro-organisms, which, through the food chain, increases the number of shrimplike krill and even birds,” Ken Smith, a marine biologist at California’s Monteray Bay Aquarium Research Institute and the study’s lead researcher, told the Toronto Star Friday.

As they grow, the plankton and algae take up carbon dioxide from the atmosphere that has dissolved into the sea water. As organisms consume the now plentiful plankton and algae, they create waste in the form of organic carbon that eventually settles on the sea floor — almost like a natural carbon sequestration program, Smith explained.

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The researchers conducted three month-long cruises to the Weddell Sea, part of the Southern Ocean, the southernmost tip of the Atlantic Ocean, just off the coast of Antarctica, in 2005, 2008 and 2009. The area is known as “iceberg alley” for its inhospitable climate.

Using remote controlled aircraft, boats, small submarines and GPS, the team tracked icebergs as they drifted northward after calving off the Antarctic ice sheet.

Every year, global climate change causes thousands of icebergs to break off from shrinking Antarctic ice shelves and drift northwards into the Weddell Sea.

As the icebergs drift and melt, iron contained in sediment — collected by the ice tens of thousands of years ago when glaciers moved over land — is released, sometimes creating trails of nutrient-rich clouds in the sea nearly 20 kilometres long.

The researchers used a device called a “Lagrangian sediment trap” that sinks to about 600 metres below the ocean surface while an iceberg floats above. The instrument then rises to the surface, collecting sediment, algae and other debris left in the wake of the iceberg.

Scientists have calculated that the melting icebergs deposit up to 120,000 tonnes of biological material into the Southern Ocean every year. That material, in turn, is believed to spur the growth of enough plankton to remove more than two billion tonnes of carbon dioxide from the air.

Smith said the phenomenon may have implications for global climate models.

“We’re essentially measuring the amount of organic carbon that is being exported,” he said. “But it’s too early to tell if this is having any impact on the overall atmosphere.”

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